Nuclear Reactor Lasers: From fission to photon (2019) | Hacker News Reader

Nuclear Reactor Lasers: From fission to photon (2019)

toughsf.blogspot.com

67 pointsrbanffy10 comments

I wonder if this could be used to create a hybrid fission-fusion plant based on inertial confinement. Use a small fission reactor to run a much larger fusion reactor. Sort of like a staged thermonuclear bomb, but controlled.

Inertial confinement fusion could generate power right now if we had amazingly efficient lasers.

> Inertial confinement fusion could generate power right now if we had amazingly efficient lasers.

Here's a funny thing: inertial confinement could be used for fission too. With inertial confinement you essentially create a mini-thermonuclear bomb. A mini-fission bomb would work too, and I think the barrier to achieve that would be much lower.

One could say this is not a big deal. It actually is. Compressing a quantity of a few grams of plutonium to become critical can't be done with conventional explosives, but it can be done via inertial confinement. And that compression could be so high that the fission could be very nearly complete. In contrast, the current state of technology is that fusion by inertial confinement barely achieves ignition, but only a tiny fraction of the fusion fuel (the deuterium-tritium mix) actually burns.

Wait... so if you stuff a few grams of enriched Plutonium into a Z-pinch device you can make it go boom?

That is interesting. A near-complete fission burn would be clean. The problem is that you need conventional reactors to get Plutonium, and extracting it and handling it is difficult and expensive.

Will it work with enriched Uranium?

Enriched uranium would work too. But enriched uranium is roughly speaking the ideal fuel for fission reactors, because it has a large ratio of delayed neutrons vs prompt neutrons. Plutonium has a much lower ratio (about one third of U-235), so plutonium is inherently harder to control. That's why plutonium is not used directly as fuel, but it's used in a mix with uranium (the so-called MOX = mixed oxide fuels). In a design based on mini-fission bombs, you don't care about control, because control is about not letting the reactivity of the core go too high, while here you want it to be as high as possible.

folks are working on those efficient lasers - e.g. https://xcimer.energy

Presumably, the energy output from a fusion plant (if we ever get there) should be self-sustaining. For starting up, I’m guessing the plant can draw power from the grid itself, no?

This depends upon the approach. The person you replied to mentioned inertial confinement. If this is used, we'll get pulses that each need to be triggered (with energy gain). Other approaches (e.g. conventional tokamaks) aim to produce a continuous stream of energy.

The second fusion stage of a thermonuclear bomb runs off the x-rays emitted by the fission primary.

A non-exploding nuclear reactor produces nowhere near the required amount of x-rays.

Or just optimize the wavelength and put photovoltaics on its path to get more efficient fusion power. Which has been proposed (without the fusion laser part) to replace RTGs in space: https://en.wikipedia.org/wiki/Optoelectric_nuclear_battery

These nuclear zealots won't stop until they create a Death Star capable of destroying planets

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